A novel hypothesis for the pathogenesis of the chronic vascular proliferative complications of human diabetes involving glycation- inactivation of the complement regulatory protein CD59 is proposed in this application. It is postulated that glycation-inactivation of CD59 results in increased deposition of the membrane attack complex (MAC) of complement, increased MAC-induced release of growth factors from endothelium and abnormal cell proliferation in the vascular wall. Consistently, MAC deposits are present in glomerular, corneal and vascular tissue of diabetic patients. The applicants have recently established a link between the presence of the MAC on cell surfaces and cell proliferation by demonstrating that MAC insertion into the membrane of endothelial cells causes release of bFGF and PDGF, two potent growth factors that stimulate proliferation of the vascular wall. The complement regulatory protein CD59 protects cells from homologous MAC insertion but this protective activity is abrogated by glycation. This is probably due to the presence within the active site of human CD59 of the glycation motif K41-H44, which is not present in any other species. This peculiarity of human CD59 could well explain the unique propensity of humans to develop proliferative diabetic complications, as it is proposed to investigate in this application. Under Specific Aim 1, measurements of CD59 glycation in urine, red blood cells and endothelium of diabetic and control subjects will be performed chemically and immunologically. Glycation-inactivation of CD59 should increase MAC deposition and MAC-induced growth factor release from endothelium, and also MAC-induced lysis of red cells. MAC-deposition and growth factor release will be assessed directly in arteries and veins obtained from subjects undergoing peripheral vascular surgery and MAC-induced lysis will be studied in red cells. Under Specific Aim 2, biochemical and site-directed mutagenesis studies will be conducted to determine whether K41 is indeed the glycated residue in CD59, and to show that mutation of the glycation motif renders CD59 resistant to glycation. Confirmation of the central hypothesis of this proposal will provide a molecular explanation for the unique propensity of humans to develop vascular complications of diabetes, and will allow the future design of molecular engineered animal models for proliferative vascular complications of diabetes. Such animal models, which do not currently exist, will help better understand the pathogenesis of the vascular complications of human diabetes and further the development of new therapeutic modalities based perhaps on complement modulation.